path: root/kernel
diff options
authorPeter Zijlstra <a.p.zijlstra@chello.nl>2009-06-19 17:39:33 +0200
committerIngo Molnar <mingo@elte.hu>2009-06-19 17:57:36 +0200
commitb49a9e7e72103ea91946453c19703a4dfa1994fe (patch)
tree7e9e74881384c581afca56cc397901f71e904c8b /kernel
parent0c87197142427063e096f11603543ca874045952 (diff)
perf_counter: Close race in perf_lock_task_context()
perf_lock_task_context() is buggy because it can return a dead context. the RCU read lock in perf_lock_task_context() only guarantees the memory won't get freed, it doesn't guarantee the object is valid (in our case refcount > 0). Therefore we can return a locked object that can get freed the moment we release the rcu read lock. perf_pin_task_context() then increases the refcount and does an unlock on freed memory. That increased refcount will cause a double free, in case it started out with 0. Ammend this by including the get_ctx() functionality in perf_lock_task_context() (all users already did this later anyway), and return a NULL context when the found one is already dead. Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: Mike Galbraith <efault@gmx.de> Cc: Paul Mackerras <paulus@samba.org> Cc: Arnaldo Carvalho de Melo <acme@redhat.com> LKML-Reference: <new-submission> Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'kernel')
1 files changed, 5 insertions, 6 deletions
diff --git a/kernel/perf_counter.c b/kernel/perf_counter.c
index 8d4f0dd41c2..adb6ae506d5 100644
--- a/kernel/perf_counter.c
+++ b/kernel/perf_counter.c
@@ -175,6 +175,11 @@ perf_lock_task_context(struct task_struct *task, unsigned long *flags)
spin_unlock_irqrestore(&ctx->lock, *flags);
goto retry;
+ if (!atomic_inc_not_zero(&ctx->refcount)) {
+ spin_unlock_irqrestore(&ctx->lock, *flags);
+ ctx = NULL;
+ }
return ctx;
@@ -193,7 +198,6 @@ static struct perf_counter_context *perf_pin_task_context(struct task_struct *ta
ctx = perf_lock_task_context(task, &flags);
if (ctx) {
- get_ctx(ctx);
spin_unlock_irqrestore(&ctx->lock, flags);
return ctx;
@@ -1459,11 +1463,6 @@ static struct perf_counter_context *find_get_context(pid_t pid, int cpu)
ctx->parent_ctx = NULL; /* no longer a clone */
- /*
- * Get an extra reference before dropping the lock so that
- * this context won't get freed if the task exits.
- */
- get_ctx(ctx);
spin_unlock_irqrestore(&ctx->lock, flags);